I have the same setup.. and in really hot weather I get warm.. I built custon dash Air for my DEV bus... my bluebird. I have researched several things..
first off make sure that rear unit is working as it should.. in my case mine appeared to "work". but I could tell it wasnt right.. I found over 8 ounces of extra oil and dye and stop leak crap in my system from when the schools had obviously kept recharging it..
I cleaned the coils (inside and out)evacuated, flushed, re-oiled, and recharged it to spec and my vent temperatues dropped 20-25 degrees lower than what they were.. so I actually get COLD air and not just cool air now..
dirty coild in and out are very common and will make a unit not work.. (esp a carrier or trans/air) because they suck the air over the inside coils instead of blow it.
you CAN move that unit to the front of the bus.. it will take some work.. those units are hung through the roof... so you'll have holes to plug.. you also have to route the freon lines in and bring them up to the front of the inside unit.. .. many of those units are set up so the linesets come into them from inside the bus walls.. and the drain lines go out as well.. you dont have to conceal the lines.. most of them are done that way..
the biuggest caveat is banging your head on the thing if you mount it across the front of the bus.. ..
im guessing its a unit with 2 blowers and 4 vents across the panel? you can cut out.the plastic of the cover and run ducts.. it shoiuld work just fine as long as you use large enough and something smooth.. (flexible ducting will tend to restrict the airflow).. the plastic pieces like are used to hide freon lines actually make pretty good ducting.. and can be bought in many sizes..
diversitech makes the parts that i use for this purpose in my DEV bus..